Assessment of gonad staging systems and other ... - CiteSeerX

eggs are spawned by females in multiple batches (McPherson 1993), and oocytes of varyingdevelopmental stages are present within the ovary at the same time (pers. obs.). Thisasynchronous development of the ovary (Wallace and Selman 1981) is common in otherexploited species of fish that inhabit tropical marine waters, and the staging systemsdescribed in this report may also be relevant to these. However, for species of fish withovaries in which oocytes develop and are spawned as one single group (synchronousdevelopment) or as two or more homogenous groups (group synchronous development), thestaging systems for S. commerson may be inappropriate.2.0 Methods2.1 Collection of samplesFresh gonad samples were collected by Fisheries WA personnel onboard commercial andrecreational vessels and from recreational fishing competitions. Frozen samples were alsoobtained from commercial and recreational fishers. Most of these samples came from thevicinity of Broome, Port Hedland, Dampier and Carnarvon, with others collected lessfrequently from Exmouth, Denham, Geraldton and Cervantes (Figure 1, Table 1).Fresh samplesLength and weight (kg) were obtained for each fish. Fork length (FL) of all fish and, wherepossible, total length (TL) were measured (all lengths in this study are mm). Total lengthswere measured to the tip of the dorsal fork of the tail, with the tail laid flat in the normalswimming position and the forks compressed slightly towards each other to remove ‘play’ inthe tail. If the dorsal tip was damaged then TL was taken to the ventral tip, although this isusually shorter and required appropriate adjustment to the equivalent dorsal forkmeasurement. Note that TL is not as precise a measure as FL in S. commerson.Measurements of the head (tip of the mouth to the firm edge of the operculum) and of thejaw (tip of the mouth to the posterior edge of the upper jaw (premaxilla)) were also taken.Where possible, the whole weight, clean weight (viscera and gonads removed), and headweight (including gills) of each fish were also obtained (body weight to 0.1 kg, head weightto 0.1 gm). Refer to the Appendix A for detail of the data sheet used to record informationwhilst in the field.Fresh gonads were usually removed from the fish within a few hours of capture, and theirsex and stage of reproductive maturity determined using a macroscopic staging system(Appendix B). Gonads obtained from recreational fishers could usually be weighed fresh(0.01 gm). Two or three transverse cuts were then made through each gonad to ensure properfixation before placing them into a perforated cellophane bag and then into plastic drumscontaining 10% formalin in seawater. If space permitted, the whole gonad was preserved,otherwise an 8 cm long mid-section of one lobe was saved.Frozen samplesFrozen samples obtained from commercial fishers comprised the head, gut and gonad ofeach fish, whereas frames (fillets removed) were obtained from recreational fishers. Samples4 Fish. Res. Rep. West. Aust.2001, 136, 1-32